1. Field of the Invention
The present, invention relates to battery-charging systems for electrical equipment. More particularly, the present invention relates to a battery-charging system that includes an electric power tool operating on rechargeable internal batteries and a battery charger for charging the internal batteries of the electric power tool.
2. Description of the Related Art
One type of conventional rechargeable electric power tool incorporates a detachable battery pack mounted in the lower end of the handle thereof. When the battery pack needs to be recharged, it is detached from the handle of the tool and set on a separate charger. After the charging is completed, the battery pack is mounted back in the handle to resume operation. If an electric power tool operating on a detachable battery pack is used for extended periods of time, for example, on a production or assembly line of an automobile plant, an auxiliary battery pack is set in a charger for recharging. When the pack mounted in the tool is discharged, the operator replaces it with the one that has been recharged by the charger and sets the discharged battery pack on the charger for recharging.
Battery packs used for the above-described purpose are generally designed to maximize their capacity and thus the operating time of the tool per charge. This tends to increase the size and weight of the packs, which in turn places an excessive physical strain on the operator and reduces the operability of the tools and work efficiency. This tendency is particularly pronounced when such large and heavy battery packs are used on assembly lines for an extended period of time; the operability of the tools may be severely affected so as to significantly reduce the productivity of the plant. In addition, loss of time in the process of replacing discharged battery packs has been a significant factor that reduces work efficiency.
Moreover, chargers used for such battery packs continue to supply charging current, even after the battery packs are charged to the full, therefore placing the batteries or cells in the pack under heavy load and reducing the charge efficiency. In addition, this results in a waste of power.
In view of the aforementioned problems, the applicant has proposed a battery-charging system as shown in FIG. 8. This battery-charging system includes a charger 1 and an electric power tool 2 which has a built-in batteries 6. According to this system, the batteries 6 can be charged without their removal from the tool 2. The electric power tool 2 additionally includes a controller 28 which in turn is provided with a central processing unit (CPU), a battery temperature sensor 8, and a current detector 10 for detecting the amperage of the charging and discharging currents of the batteries 6, which permit. monitoring of the remaining charge level based on the charging/discharging current. Also provided in the tool 2 are four terminals 13a, 14a, 15a, and 16a. The terminals 13a and 14a are provided for carrying current to charge the batteries 6, the terminal 15a is provided for outputting to the charger 1 data on the temperature of the batteries 6, and the terminal 16a is provided for outputting to the charger 1 the data on the charge/discharge level from the controller 28. The charger 1 is provided with four corresponding terminals for connection with these terminals 13a, 14a, 15a, and 16a so as to control charging operation based on data on battery charge/discharge received from the controller 28 and on the temperature of the batteries, and to indicate the charge/discharge level of the batteries.
Furthermore, the charger 1 includes a charge/discharge circuit 29, an indicator unit 4 for indicating the charge state and the remaining charge level of the batteries, and a cooling fan 5. Also included are the aforementioned four terminals that are connected to the terminals 13a, 14a, 15a, and 16a of the electric power tool 2 when it is set on the charger 1. These charger terminals comprise a pair of terminals 13b and 14b for passing charging current to the electric power tool 2, a data receive terminal 16b for receiving data on the charge/discharge level of the rechargeable batteries 6, and a temperature terminal 15b provided for receiving data on the temperature of the rechargeable batteries 6.
As described above, since this system permits charging of batteries without their removal, charging operation itself becomes much less troublesome, and the rechargeable batteries can always be charged to the full when the tool is not in use. Therefore, the charge capacity of the batteries can be reduced so as to reduce the weight of the tool itself. According to the system, by monitoring the remaining charge level, the operator can maintain the torque produced by the tool within a preferred range, which makes the system particularly useful when used on assembly or production lines in plants.
The installed controller transmits information on the charge/discharge level and on the battery temperature to the charger, allowing the charger to indicate the charge state of the batteries and to vary the charging current to suit the charge state. This enables efficient use of the batteries and enhances work efficiency.
Rechargeable batteries, such as nickel-cadmium (NiCad) batteries, deteriorate or have the property of decreasing in capacity if left unused for prolong periods of time or subjected to repeated charge and discharge at less than their full capacities. Since rechargeable batteries are consumable articles, their charge capacities gradually decrease over time, even if care is taken. This results in production of insufficient torque by tools, even after a full charge, and/or in discrepancies between the data on the remaining battery level stored in the aforementioned controller and the actual battery level, thus reducing the reliability of the charge level information provided by the system.